1. Field of the Invention
The present invention relates to a corrosion-resisting ceramic material having high resistance to corrosive halogen-based gases and, more particularly, to a halogen-plasma resisting member in a plasma processing apparatus.
2. Prior Art
The halogen plasma technology is utilized in a semiconductor fabricating process, discharging tubes and lamps. The plasma in a corrosive halogen-based gas containing fluorine and/or chlorine, which has high reactivity, is utilized to facilitate growth from the gas phase, etching and cleaning during fabrication of a semiconductor device. By way of example, a halogen plasma device includes a CVD device or a sputtering device for formation of a film on a semiconductor wafer, and an etching device for micro-fabrication of a semiconductor wafer.
Such members which are exposed within any of those devices are required to have a high resistance to corrosion because they are apt to contact the corrosive gas of a halogen or the plasma of such corrosive gas. Hitherto, those members are made of a SiO2 material such as glass or quartz, and a corrosion-resisting metal such as stainless steel or monel metal is also used therefor.
The members made by the use of such a corrosion-resisting material may include, for example, an inner wall, a manhole, a microwave intake port and jigs which are utilized within the plasma processing apparatus used for the production of semiconductor devices and/or liquid crystals. Such members may include a discharging tube utilizing a halide gas and a discharge wall of a metal halide lamp other than the plasma processing apparatus.
As an exemplary device utilizing a plasma of a halogen gas, FIG. 6 illustrates a CVD device for forming the semiconductor wafer, including a microwave generating chamber 61 and a processing chamber 62 with a microwave introducing window 63 serving as a partition wall that separates the microwave generating chamber from the processing chamber. A coil 64 is disposed around an outer periphery of the processing chamber for forming an electromagnetic field. The processing chamber has a gas supply port 65 for the supply of a film forming gas, including a halogen gas, and an atmospheric gas, a gas discharge port 66 for the discharge of the gases, and an observatory window 67 for monitoring the inside.
In the processing chamber 62, there is provided an electrostatic chuck 70 for holding a semiconductor wafer 50. The electrostatic chuck includes a disc-shaped insulating base plate 71 having an electrode 73 embedded therein for sucking the wafer onto a support surface 72 of the base plate by the effect of an electrostatic force. A heater 74 is positioned below the base plate.
In this CVD device, the wafer is held by the electrostatic chuck in the processing chamber 62, in which the atmosphere is conditioned and microwaves from the microwave generating chamber 61 cooperate with the electromagnetic field, produced by the coil, to excite a film forming gas in the atmosphere so that a film forming gas plasma including a halogen gas can be generated to form a film on the wafer.
Within this type of the device for since the inner wall 68, the observatory window 67, the microwave introducing window 63 and the electrostatic chuck 70 are exposed to the highly corrosive plasma, they are formed of a corrosion-resisting material. For those members, a sintered body of alumina, sapphire or aluminum nitride AIN has hitherto been employed because of its excellent corrosion resistance (such as disclosed in, for example, the Japanese Patent Publication JP-A 5-251365), and members surface-coated with this material by the use of a CVD method are employed as well. In addition, for those members, a heater coated with graphite or boron nitride is also employed.
However, glass or quartz which have hitherto been used, exhibit an insufficient corrosion resistance in the plasma and are quick to wear. In particular, there has been a problem in that a contact surface when contacting a plasma of chlorine tends to be etched off, accompanied in change in surface property and that in the case of a member that requires a light transmissivity, the light transmissivity tends to be lowered as a result of the surface progressively fogged up. Even the members utilizing a metal such as stainless steel has so insufficient a corrosion resistance as to constitute a cause of occurrence of rejected products during the manufacture of semiconductor devices due to corrosion.
Also, even with the conventional sintered body of alumina, sapphire or aluminum nitride, the surface tends to be corroded in contact with the chloride plasma to such an extent that no separation of crystalline particles forming the surface can be avoided, and fine particles separated from the surface will stick to a support surface of the electrostatic chuck and the semiconductor wafer with the film forming accuracy consequently affected badly.
Moreover, inconveniences have been encountered that affected by a physical influence, brought about by, for example, light, heat and/or ions generated in the plasma within the device, and/or a chemical reaction with active species and the corrosive gas, a transparent windowpane for the windows is susceptible to progressive surface corrosion and consequent surface fogging to such an extent that observation of the interior of the device and analysis of the plasma will no longer be carried out. For this reason, a situation has arisen that there is no way other than to install the window material at a location distant from the plasma.
An alumina-coated glass material disclosed in the Japanese Laid-open Patent Publication No. 8-27566-A has been found having problems in that alumina itself has an insufficient resistance to corrosion brought about by the halogen plasma and that because of a difference in coefficient of thermal expansion between the alumina film and the glass base, not only does separation of the film tend to occur, but also the film is susceptible to cracking.
Particularly in the semiconductor manufacturing industry, with advance of the large scale integration of semiconductor integrated circuits, a high-density halogen plasma comes to be used widely and, because of the conventional window material having a relatively short lifetime, demands have arisen to make available a window material having high resistance to corrosion by the halogen plasma and also an excellent light transmissivity.
An object of the present invention is to provide a ceramic material having increased resistance to corrosion in a plasma of a corrosive halogen-based gas.
Another object of the present invention is to provide a member having increased resistance to corrosion in plasma of the corrosive halogen-based gas.
An further another object of the present invention is to provide a transparent member having increased resistance to corrosion in the plasma of the corrosive halogen-based gas.
A further another object of the present invention is to provide a member resistant to the halogen plasma, which can be employed in a plasma processing device utilizing the halogen plasma.
In order to accomplish these objects of the present invention, the ceramic material according to the present invention makes use of a composite oxide of metals comprising an element of Groupe IIa or IIIa in the Periodic Table and Al and/or Si.
The ceramic material made up of such a composite metal oxide forms a chloride of a high melting point on the surface thereof, as the reaction proceeds with a plasma of a corrosive chlorine based gas, the chloride developing into a stable chloride layer on the surface, thereby suppressing the progress of corrosion in the member. In this way, the ceramic material of the present invention can exhibit higher resistance to the halogen plasma than that exhibited by the conventional alumina or aluminum nitride. The ceramic material of the present invention makes it possible to provide at a relatively low cost a member capable of showing high corrosion resistance for a prolonged period of time even if it is used in the highly dense corrosive atmosphere rich of chlorine or fluorine.
The ceramic material may contain metallic impurities, other than the metal components used to form the composite metallic oxide, in a total amount of 0.1 wt % or less. Regulating the content of the metallic impurities is effective to avoid a possible separation of crystalline particles from the surface, which would otherwise occur as a result of corrosion attributable to impurities, while the member is exposed to the halogen plasma and, hence, to allow the ceramic material to exhibit a further resistance to corrosion. This is particularly effective to suppress possible occurrence of the contaminated semiconductor devices during manufacturing by use of the plasma processing apparatus.
The member resistant to the halogen plasma according to the present invention may be made of a sintered material of the composite metal oxide comprising the elements of Groupe IIa or IIIa in Periodic Table and Al and/or Si. The sintered material may be utilized to form a corrosion-resisting layer only on the surface portion of the member which is exposed to the halogen based plasma.
A member of the present invention is selected to be a sintered material of yttrium-aluminum-garnet (hereinafter referred to as xe2x80x9cYAGxe2x80x9d) from among the composite metal oxides of an element of the Group IIIa in Periodic Table and aluminum and/or silicon, to be subsequently formed into a desired shape. In order that the member of the present invention has a surface with increased resistance to corrosion, low inner porosity and smoothness of the polish surface may be defined for the YAG sintered body. More specifically, the sintered body for the member of the present invention is defined such that a YAG sintered body has a porosity of 3% or less, and a center line surface roughness Ra of 1 xcexcm or less, which is measured according to JIS B 0601.
Furthermore the YAG sintered body of the member of the present invention may be defined to contain an oxide of a metal of Group IIa in Periodic Table and silicon oxide in a total amount of 0.15 wt % or less, this increasing an resistance of the member relative to corrosion due to the halogen-based gas plasma.
A transparent or light transmissive member of the present invention may be formed of a light transmissive YAG having a thickness within a range of 0.5 to 10.0 mm. This member may comprise a transparent substrate having a coated or sintered layer of YAG formed on one of surfaces which is exposed to the plasma. In such case, the coated or sintered layer may have a thickness in a range of 0.1 to 10.0 mm. The YAG sintered body is effective to allow the transparent member to retain the resistance to corrosion due to the halogen-based plasma and also to not reduce in transparency. The use of the member as a window material is effective to allow the window to function as a window due to the light transmissivity and also to avoid lowering of the light transmissivity which would otherwise occur as a result of the surface of the window material being corroded in contact with the plasma, thereby making it possible to prolong the lifetime of the window member.
These transparent or light transmissive members may be used for viewing windows for the plasma processing device and transparent envelopes forming a part of discharging tubes such as electric lamps.
Furthermore, the corrosion-resisting member of the present invention may include a MgO-containing ceramic sintered body comprising, on an oxide basis, MgO in a amount of 15 wt % or more and Al2O3 in a amount 85 wt % or less, since the MgO-containing ceramics has its high corrosion resistance to the plasma of the halogen gas. This ceramic material may comprise a ceramic sintered body comprising any of crystal phases of MgO, MgAl2O4 and MgO, MgAl2O4, and, MgAl2O4 and Al2O3, which have an average crystal grain size of 3 xcexcm or more and a porosity of 0.2 % or less.